1. Field of the Invention
The present invention relates to an optical data link which is easy to manufacture, and has high mechanical reliability and high performance, and a method of manufacturing the same.
2. Related Background Art
Conventional optical data links are disclosed in U.S. Pat. Nos. 5,127,073 and 5,475,783, and U.S. patent application Ser. No. 08/552,351, is now issued to U.S. Pat. No. 5,742,480, whose basic Japanese Application Laid-Open number is 8-136,767.
In the optical data link called SSL which is disclosed in U.S. Pat. No. 5,127,071, a lead frame having a board portion on which electronic parts are mounted, and lead pins and a metal optical connector, in which the optical element (light-emitting or light-receiving element) having undergone optical axis alignment with the optical fiber is sealed, are prepared. And the lead frame and the optical connector are integrally formed with a resin.
In the optical data link called Kurashima Model which is disclosed in U.S. Pat. No. 5,475,783, a sleeve and a link housing (side plate) are integrally formed with a resin, and an optical element (light-receiving element) is mounted on a circuit board independently of the sleeve and the link housing. With this structure, optical axis alignment between the optical element and the optical fiber in the sleeve is performed by fitting the circuit board with a predetermined portion of the link housing. In addition, a lens for focusing an optical signal sent from the optical element onto the incident end of the optical fiber is placed in the sleeve. This lens is formed separately from the link housing.
In the optical data link disclosed in U.S. patent application Ser. No. 08/552,351, is now issued to U.S. Pat. No. 5,742,480, an optical element (light-emitting diode or semiconductor laser) having undergone optical axis adjustment is mounted on a board (head portion), and the electronic circuit is mounted on another board (main body portion). These boards are electrically connected by using a flexible printed board. In addition, optical axis alignment between the optical fiber and the optical element is performed by fitting the optical element in element insertion holes formed in sleeves.
Optical axis adjustment between an optical fiber and a light-emitting element in a transmission section and optical axis adjustment between an optical fiber and a light-receiving element in a reception section are critical to an optical data link.
In addition, in an optical data link in which transmission and reception sections are integrally assembled, positional adjustment between the transmission and reception sections is also important. More specifically, in the reception section, it suffices if optical axis alignment between the optical fiber end from which an optical signal emerges and the light-receiving element for receiving the optical signal is performed on the submillimeter order. In contrast to this, in the transmission section, a very high positioning precision on the micron order is required for optical axis alignment between the major surface of the light-emitting element for emitting an optical signal and the optical fiber for receiving the optical signal. As described above, since the positioning precision required for the transmission and reception sections greatly differ from each other, technical difficulty has been posed in realizing an optical data link in which transmission and reception sections are integrally assembled.
In a recent ultra-high-speed optical data link, to satisfy the requirement for fast response characteristics, the light-receiving area of a light-receiving device tends to be decreased, and hence an optical axis alignment precision on the micron order has also been required for the reception section.
In the SSL type optical data link, such positioning adjustment is performed as follows. Optical adjustment between the light-receiving element and the optical fiber and between the light-emitting element and the optical fiber in the metal optical connector is performed with a precision on the micron order while optical coupling between the light-receiving element and the optical fiber and optical coupling between the light-emitting element and the optical fiber are actually monitored. Thereafter, the light-receiving and light-emitting elements are fixed in the metal package by resin sealing, thereby performing positioning between the optical axes of the transmission and reception sections. The positioning precision between the optical axes of the transmission and reception sections is therefore determined by the precision of a mold for resin sealing.
In this positioning adjustment method, however, the metal package is expensive. In addition, when a defect is caused in the resin sealing process, even a normally operating optical connector must be discarded, posing a problem in terms of yield and the like. Furthermore, wire bonding must be used to connect the board portion, on which the electronic circuit is mounted, to the optical connector, and the distance therebetween must be several millimeters or more. The parasitic inductance and the like of the bonding wires therefore adversely affect the high-speed operation of the device.
In the Kurashima Model optical data link, the light-receiving and light-emitting elements are mounted on the board on which the electronic elements constituting the electronic circuit are mounted. This device uses a mechanism of performing macro-positioning of this board and the housing of the optical data link to simultaneously perform optical axis adjustment.
According to this mechanism, the precision between the optical axes is determined by the positioning precision in mounting the light-receiving and light-emitting elements on predetermined portions on the board and the positioning precision in mounting the board on the housing, i.e., the positioning precision at the two positions. For this reason, all the components must be processed with very high precision. A problem is therefore posed in terms of yield and the like. In addition, this mechanism has no means for finely adjusting the positions of the sleeve for holding the optical fiber and the light-receiving and light-emitting elements.
Furthermore, in this mechanism, since the board is mounted on the housing, and the light-receiving and light-emitting elements are mounted on the board, fine adjustment is basically performed at two portions with reference to the housing. For this reason, if an external force acts on the housing, and the housing as the reference mechanically deforms during an operation, an optical axis shift may occur.
Moreover, since the light-receiving and light-emitting elements and the electronic elements are mounted on the same board, the mounting area is limited by the volume of the housing, posing difficulty in realizing high performance by mounting many electronic elements.
In the optical data link disclosed in U.S. patent application Ser. No. 08/552,351, since the board on which the light-receiving and light-emitting elements are mounted is separated from the board on which the electronic elements are mounted, the number of electronic elements mounted is not limited. However, the electronic circuit constituted by the electronic elements must be connected to the light-receiving and light-emitting elements through interconnections. For this reason, the parasitic inductance and the like of the interconnections adversely affect the high-speed operation of the device. In addition, since the respective boards are separated from each other, the number of parts increase, resulting in a deterioration in productivity.
The present invention has been made in consideration of the above problems in the conventional techniques, and has as its object to provide a high-performance optical data link with high mechanical reliability which can be easily manufactured, and a method of manufacturing the same.